Dermal hypersensitivity reactions to imported fire ants.

A survey of suburban residents of New Orleans, La., revealed that 58% of the individuals who responded had been stung by imported fire ants (IFA) within the previous year. More than half of the patients stung had dermal reactions that were distinct from the previously reported reactions to IFA in that immediate wheal-and-flare reactions evolved into pruritic, edematous lesions that persisted about the developing pustule for 24 hr or more. Twenty-one volunteers were stung with live IFA, and the course of the reactions was observed. Nine developed persistent reactions after stings. These reactions could be reproduced by the intradermal injection of IFA--whole body extract in only four of these nine subjects. Biopsy specimens of sting reactions at 6 hr demonstrated the reactions to be "late phase reactions" characterized by dense fibrin deposits like those previously noted in dermal reactions to ragweed and insulin. Eosinophils were present in the sting-associated pustules only in individuals who developed late-phase reactions. These data demonstrate that late-phase reactions occur commonly to IFA stings and that this form of insect hypersensitivity may not always be diagnosed by skin testing with whole body extract.